PART II : BI-AMPING

Using the Switchblade it is a simple matter to create parallel/series biamped networks. Bi-amping is similar to how a frequency crossover is used to get the best performance out of power amps (where two amps/speaker sets share the workload between low and high frequency sounds) but in this case, the improvement is overdriven tone, and the workload sharing is between two preamps:

In preamp bi-amping, the guitar signal is split with one signal going to a graphic or parametric (preferred) EQ device set to reduce all high frequency notes and only pass the fundamental frequencies of low and middle notes. The output of the EQ is then fed to a guitar preamp set for an appropriate amount of overdrive. Likewise the second guitar signal also goes to an EQ set to attenuate all low and middle notes and only pass upper frequency notes. Its output is then fed into a second preamp also set to sound good alongside the first. Finally the signals from the two preamps are mixed together and sent to the main amplifier. The main amp should be a clean, hi powered amp, a solid state (MOS type) amp would not be unusual here or a tube stack set on the clean channel. Keep in mind that all overdrive is done in the preamps and not in the final amp.

This setup allows high frequency notes to achieve the full benefit of their own overdrive channel without having to deal with the overbearing lower frequencies which are processed separately. The result is a very smooth tone with lower overall intermodulation distortion and very high sensitivity (sensitivity is the ability of an amp to produce comparable distortion tones across a wide range of volume dynamics. (More below)

Multiple Power Amps

In addition if you are using two main amplifiers, then instead of mixing the two signals from the preamps together, try sending the signals to separate amps for an even richer sound. Using realtime control techniques, an interesting addition to this dual amp setup would be to bypass both EQs with a dry signal assigned to a continuous controller. As the controller is moved down, the amount of EQ is reduced and at the extreme, both preamps and both main amps are getting the same full bandwidth signal.

Using a Switchblade, multi amp operation can be taken to new heights since the guitar signal can be sent through several effects before going out to individual amplifiers, or alternately, tapping off different points in a complex effect network, remixing to new levels and with other tap points and finally to separate amplifiers. Combine this with continuous control to allow more interaction between amps and the result can be extreme.

With the Switchblade's ability to split a guitar signal and route the signal to different outputs, multi amp setups are a simple matter. More importantly, a guitar signal can be split and sent to multiple preamps in parallel, and then the returns from the preamps can be routed to multiple amplifiers on stage, enhancing the multi amp soundfield further.  (more below)

Bi-Amping Theory

To understand how bi-amping improves sound, it's important to understand the way overdrive works on a guitar signal, beyond the way that distortion increases with input signal strength. On closer examination, what is really happening is that a preamp changes the shape of the audio signal more at the extremes of the signal (the positive and negative most excursions of the actual audio waveform) and very little at the "zero crossing point" or the resting area. Therefore, if a guitar is played hard, (higher signal level) it will distort more than if played softly. If the difference in distortion between softly played notes and notes played hard is minimal, without losing dynamic range, then the amp is said to have "high sensitivity", a very desirable feature. The key word here is dynamic range. It is a simple matter to simply crank the drive up on a preamp so that both soft and loud note distort equally, but the overall loudness of the soft and loud notes will be the same. This is the sound most typically used in "speed metal" and shred styles. A preamp driven to this extent has low sensitivity. High sensitivity, high dynamic range sounds are evident in the setups used by such artists as Stevie Ray Vaughn, Neil Young, and Mark Knopfler.

To make matters more difficult, low notes on a guitar have higher excursions (peak to peak signal strength) than do high notes on a guitar. When both high and low notes are played on a guitar (a chord), then a low level upper note is mixed in with a high level lower note. At the extremes of the low frequency excursions, the higher notes literally get the life sucked right out of them. As the low frequency note passes through the zero crossing point the higher frequency notes can once again breathe. In worst case scenarios the result of this phenomenon is a tinny, intermodulation type of distortion typical of cheap transistor amps or amps that have the all time lowest sensitivity. Higher sensitivity amps "spread out" the distortion of the signal over the full excursion of the waveform, allow the higher notes riding on the back of the lower notes to breathe during the full excursion of the low note resulting in the much more pleasing harmonic distortion or what is commonly referred to as a "tube" type sound.

Multiple Amplifier Theory

A basic idea of splitting a guitar signal (traditionally using a "Y" cord) and going into several amplifiers is a staple arrangement of such players as Hendrix, Trower, and many others. The reason it sounds so good is twofold. The first and most obvious reason is that you can use several lower powered amps (such as 50 watt heads) which are more easily overdriven to create a sound that is larger than using a single high powered amp which is not so easily clipped for a given sound pressure level. The other and not so obvious reason is the interaction of the audio wavefronts between speaker cabinets. In a hypothetically ideal situation, the sound coming from one speaker cabinet would be identical to the sound coming from all the others. The result would be a strong sound directly in front of the cabinets and a weaker sound as one moves off center due to the interference of out of phase wavefronts. In the real world, however, each cabinet puts out a sound quite different (different harmonic structure) than its neighbor due to differences in cabinets, speakers, and amplifiers and even its position on the stage. The result is a much more complex interaction between the audio wavefronts and an overall sound of much greater "depth". For those of you who are familiar with a "hologram", the theory is the same. A hologram (when viewed in normal lighting) is nothing but a smoky photo of light and dark circles or "wavefronts". This would be equivalent to one amplifier on stage. When a Laser beam (another wavefront) is passed through a hologram, the two groups of wavefronts interact with each other and the result is a striking three dimensional image appearing out of nowhere and sitting in space. Likewise, when finely tuned sounds (wavefronts created by seasoned players) come out of multiple cabinets, the wavefronts interact and the result is a kind of "surreal" imaging whose shape can be molded into a very pleasing sound simply by "playing" the wavefronts--by moving toward and away from the cabinets, bending until the right "tone" happens, tapping and bending the neck to enhance wavefront variations, subtle "wah" pedal movements to vary the harmonic structure of the wavefronts, and so on.